It has been known to form a silicon nitride film (SiN film) as an insulating film on a substrate to be processed (“substrate”) in order to protect the substrate. For example, Japanese Patent Laid-Open Publication No. 2010-87186 discloses a method of forming a silicon nitride film on a substrate through a plasma CVD method, in which microwave is introduced into a processing container through a planar antenna formed with a plurality of holes to generate plasma. In this method, as an example of a raw material gas used for depositing the silicon nitride film, trisilylamine (TSA) is mentioned. Also, International Publication WO. 2007-139140 discloses a method of forming a SiN film through a plasma CVD method in which silane (SiH4) is used as a deposition raw material gas.